The present invention is directed to lyocell fibers having a high hemicellulose content. The fibers are readily cut into staple lengths and can be spun into yarns with excellent knitting and weaving characteristics which dye exceptionally well. The fibers have a cotton-like denier.
For over a century strong fibers of regenerated cellulose have been produced by the viscose and cuprammonium processes. The latter process was first patented in 1890 and the viscose process two years later. In the viscose process cellulose is first steeped in a mercerizing strength caustic soda solution to form an alkali cellulose. This is reacted with carbon disulfide to form cellulose xanthate which is then dissolved in dilute caustic soda solution. After filtration and deaeration the xanthate solution is extruded from submerged spinnerets into a regenerating bath of sulfuric acid, sodium sulfate, zinc sulfate, and glucose to form continuous filaments. The resulting so-called viscose rayon is presently used in textiles and was formerly widely used for reinforcing in rubber articles such as tires and drive belts.
Cellulose is also soluble in a solution of ammoniacal copper oxide. This property formed the basis for production of cuprammonium rayon. The cellulose solution is forced through submerged spinnerets into a solution of 5% caustic soda or dilute sulfuric acid to form the fibers. After decoppering and washing the resulting fibers have great wet strength. Cuprammonium rayon is available in fibers of very low deniers and is used almost exclusively in textiles.
More recently other cellulose solvents have been explored. One such solvent is based on a solution of nitrogen tetroxide in dimethyl formamide. While much research was done, no commercial process has resulted for forming regenerated cellulose fibers using this solvent.
The usefulness of tertiary amine-N oxides as cellulose solvents has been known for a considerable time. Graenacher, in U.S. Pat. No. 2,179,181, discloses a group of amine oxide materials suitable as solvents. However, the inventor was only able to form solutions with low concentrations of cellulose and solvent recovery presented a major problem. Johnson, in U.S. Pat. No. 3,447,939, describes the use of anhydrous N-methylmorpholine-N-oxide (NMMO) and other amine N-oxides as solvents for cellulose and many other natural and synthetic polymers. Again the solutions were of relatively low solids content. In his later U.S. Pat. No. 3,508,941, Johnson proposed mixing in solution a wide variety of natural and synthetic polymers to form intimate blends with cellulose. A nonsolvent for cellulose such as dimethylsulfoxide was added to reduce dope viscosity. The polymer solution was spun directly into cold methanol but the resulting filaments were of relatively low strength.
However, beginning in 1979 a series of patents were issued to preparation of regenerated cellulose fibers using various amine oxides as solvents. In particular, N-methylmorpholine-N-oxide with about 12% water present proved to be a particularly useful solvent. The cellulose was dissolved in the solvent under heated conditions, usually in the range of 90xc2x0 C. to 130xc2x0 C., and extruded from a multiplicity of small diameter spinnerets into air. The filaments of cellulose dope are continuously mechanically drawn in air by a factor in the range of about three to ten times to cause molecular orientation. They are then led into a nonsolvent, usually water, to regenerate the cellulose. Other regeneration solvents, such as lower aliphatic alcohols, have also been suggested. Examples of the process are detailed in McCorsley and McCorsley et al., U.S. Pat. Nos. 4,142,913; 4,144,080; 4,211,574; 4,246,221, and 4,416,698 and others. Jurkovic et al., in U.S. Pat. No 5,252,284 and Michels et al., in U.S. Pat. No. 5,417,909 deal especially with the geometry of extrusion nozzles for spinning cellulose dissolved in NMMO. Brandner et al., in U.S. Pat. No. 4,426,228, is exemplary of a considerable number of patents that disclose the use of various compounds to act as stabilizers in order to prevent cellulose and/or solvent degradation in the heated NMMO solution. Franks et al., in U.S. Pat. Nos. 4,145,532 and 4,196,282, deal with the difficulties of dissolving cellulose in amine oxide solvents and of achieving higher concentrations of cellulose.
Cellulose textile fibers spun from NMMO solution are referred to as lyocell fibers. Lyocell is an accepted generic term for a fiber composed of cellulose precipitated from an organic solution in which no substitution of hydroxyl groups takes place and no chemical intermediates are formed. One lyocell product produced by Courtaulds, Ltd. is presently commercially available as Tencel(copyright) fiber. These fibers are available in 0.9-2.7 denier weights and heavier. Denier is the weight in grams of 9000 meters of a fiber. Because of their fineness, yarns made from Tencel(copyright) lyocell produce fabrics having extremely pleasing hands.
One limitation of the lyocell fibers made presently is a function of their geometry. They are continuously formed and typically have quite uniform, generally circular or oval cross sections, lack crimp as spun, and have relatively smooth, glossy surfaces. This makes them less than ideal as staple fibers since it is difficult to achieve uniform separation in the carding process and can result in non-uniform blending and uneven yarn. In part to correct the problem of straight fibers, man made staple fibers are almost always crimped in a secondary process prior to being chopped to length. Examples of crimping can be seen in U.S. Pat. Nos. 5,591,388 or 5,601,765 to Sellars et al. where the fiber tow is compressed in a stuffer box and heated with dry steam. It might also be noted that fibers having a continuously uniform cross section and glossy surface produce yarns tending to have a xe2x80x9cplasticxe2x80x9d appearance. Yarns made from thermoplastic polymers frequently must have delustering agents, such as titanium dioxide, added prior to spinning. Wilkes et al., in U.S. Pat. No. 5,458,835, teach the manufacture of viscose rayon fibers having cruciform and other cross sections. U.S. Pat. No. 5,417,909 to Michels et al. discloses the use of profiled spinnerets to produce lyocell fibers having non-circular cross sections but the present inventors are not aware of any commercial use of this method.
Two widely recognized problems of lyocell fabrics are caused by fibrillation of the fibers under conditions of wet abrasion, such as might result during laundering. Fibrillation tends to cause xe2x80x9cpillingxe2x80x9d; i.e., entanglement of fibrils into small relatively dense balls. It is also responsible for a xe2x80x9cfrostedxe2x80x9d appearance in dyed fabrics. Fibrillation is believed to be caused by the high degree of molecular orientation and apparent poor lateral cohesion within the fibers. There is an extensive technical and patent literature discussing the problem and proposed solutions. As examples, reference might be made to papers by Mortimer, S. A. and A. A. Pxc3xa9guy, Journal of Applied Polymer Science, 60:305-316 (1996) and Nicholai, M., A. Nechwatal, and K. P. Mieck, Textile Research Journal 66(9):575-580 (1996). The first authors attempt to deal with the problem by modifying the temperature, relative humidity, gap length, and residence time in the air gap zone between extrusion and dissolution. Nicholai et al. suggest crosslinking the fiber but note that xe2x80x9c . . . at the moment, technical implementation [of the various proposals] does not seem to be likelyxe2x80x9d. A sampling of related United States patents might include those to Taylor, U.S. Pat. Nos. 5,403,530, 5,520,869, 5,580,354, and 5,580,356; Urben, U.S. Pat. No. 5,562,739; and Weigel et al. U.S. Pat. No. 5,618,483. These patents mostly relate to treatment of the fibers with reactive materials to induce surface modification or crosslinking. Enzymatic treatment of yarns or fabrics is currently the preferred way of reducing problems caused by fibrillation. However, all of the treatments noted have disadvantages and increase the cost. A fiber that was resistant to fibrillation would be a significant advantage.
Low denier fibers from synthetic thermoplastic polymers have been produced by a number of extrusion processes. One, termed xe2x80x9cmelt blowingxe2x80x9d, is particularly relevant to the present invention. The molten polymers are extruded through a series of small diameter orifices into a high velocity air stream flowing generally parallel to the extruded fibers. This draws or stretches the fibers as they cool. The stretching serves two purposes. It causes some degree of longitudinal molecular orientation and reduces the ultimate fiber diameter. Melt blown fibers were initially formed from polypropylene but have since been made from many polymers. They are generally termed xe2x80x9cmicrofibersxe2x80x9d since their diameter is most usually less than 10 xcexcm (approximately 1 denier). There is an extensive patent and general technical literature on the process since it has been commercially important since the early 1970s. Exemplary patents to melt blowing are Weber et al., U.S. Pat. No. 3,959,421, and Milligan et al., U.S. Pat. No. 5,075,068. The Weber et al. patent uses a water spray in the gas stream to rapidly cool the fibers. A somewhat related process is described in PCT Publication WO 91/18682 which is directed to a method for coating paper by modified melt blowing. Coating materials suggested are aqueous liquids such as xe2x80x9can aqueous solution of starch, carboxymethylcellulose, polyvinyl alcohol latex, a suspension of bacterial cellulose, or any aqueous material, solution or emulsionxe2x80x9d. However, this process actually atomizes the extruded material rather than forms it into latent fibers. Zikeli et al., in U.S. Pat. Nos. 5,589,125 and 5,607,639, direct a stream of air transversely across strands of extruded lyocell dope as they leave the spinnerets. This air stream serves only to cool and does not act to stretch the filaments. French laid open application 2,735,794 describes formation of lyocell fibers by a process of melt blowing. However, these are highly fragmented microfibers useful principally for production of self bonded non-woven webs.
Extremely fine fibers, termed xe2x80x9cmicrodenier fibersxe2x80x9d generally are regarded as those having a denier of 1.0 or less. Meltblown fibers produced from various synthetic polymers, such as polypropylene, nylons, or polyesters are available with diameters as low as 0.4 xcexcm (approximately 0.001 denier). However, the strength or xe2x80x9ctenacityxe2x80x9d of most of these fibers tends to be low and their generally poor water absorbency is a negative factor when they are used in fabrics for clothing. Microdenier cellulose fibers, as low as 0.5 denier, have been produced before the present only by the viscose process.
The present process can produce a unique lyocell fiber in the cotton diameter or finer range that overcomes many of the limitations of presently available lyocell fibers, rayons, or other fibers produced from synthetic polymers. It overcomes many of the limitations of the present process for making continuous lyocell fibers. The process uses much larger spinning orifices enabling a higher dope throughput per orifice with a greatly reduced tendency for orifice plugging due to small bits of unfiltered foreign matter in the dope.
The surface of each fiber produced by the process tends to be pebbled, as seen at high magnification, and the fibers have a cross section of varying shape and diameter along their length, have significant natural crimp, are resistant to fibrillation under conditions of wet abrasion, and have excellent dyeability. All of these are desirable characteristics found in most natural fibers but missing in lyocell fibers produced commercially to the present.
With the exception of the French laid open application, processes analogous to melt blowing have never been used with cellulosic materials since cellulose itself is basically infusible. Melt blowing has never before to applicants"" knowledge been used for preparation of continuous textile denier cellulose fibers.
The present invention is directed to a process for production of regenerated cellulose fibers and to the fibers so produced. The terms xe2x80x9ccellulosexe2x80x9d and xe2x80x9cregenerated cellulosexe2x80x9d as used here should be construed sufficiently broadly to encompass blends of cellulose with other natural and synthetic polymers, mutually soluble in a spinning solvent, in which cellulose is the principal component by weight. In particular it is directed to fibers produced from cellulose solutions in amine N-oxides by processes analogous to melt blowing. Where the term xe2x80x9cmelt blowingxe2x80x9d is used it will be understood that it refers to a process that is similar or analogous to the process used for production of thermoplastic fibers, even though the cellulose is in solution and the spinning temperature is only moderately elevated. The term xe2x80x9ccontinuously drawnxe2x80x9d refers to the present commercial process for manufacture of lyocell fibers where they are extruded and mechanically pulled, first through an air gap to cause elongation and molecular orientation and then through a regeneration bath.
The processes involve dissolving a cellulosic raw material in a suitable solvent. Most usually this will be an amine oxide, preferably N-methylmorpholine-N-oxide (NMMO) with some water present. Other solvents can be used either by themselves or in admixture with NMMO; e.g., the depolymerized nylon monomers as shown in Chin et al., U.S. Pat. No. 5,362,867. Where the term xe2x80x9ccellulose solution in NMMOxe2x80x9d or similar language is used it should be understood that it is intended to be read broadly and include other suitable solvents or solvent mixtures. This dope, or cellulose solution in NMMO, can be made by known technology; e.g., as is discussed in any of the McCorsley or Franks et al. patents aforenoted. In the present process, the dope is then transferred at somewhat elevated temperature to the spinning apparatus by a pump or extruder at temperatures from 70xc2x0 C. to 140xc2x0 C. Ultimately the dope is directed to an extrusion head having a multiplicity of spinning orifices. The dope filaments emerge into a relatively high velocity turbulent gas stream flowing in a generally parallel direction to the path of the latent fibers. As the cellulose solution is extruded through the orifices the liquid strands or latent filaments are drawn (or significantly decreased in diameter and increased in length) during their continued trajectory after leaving the orifices. The turbulence induces a natural crimp and some variability in ultimate fiber diameter both between fibers and along the length of individual fibers. The crimp is irregular and will have a peak to peak amplitude that is usually greater than about one fiber diameter with a period usually greater than about five fiber diameters. At some point in their trajectory the fibers are contacted with a regenerating solution. Regenerating solutions are nonsolvents such as water, lower aliphatic alcohols, or mixtures of these. The NMMO used as the solvent can then be recovered from the regenerating bath for reuse. Preferably the regenerating solution is applied as a fine spray at some predetermined distance below the extrusion head.
Turbulence and oscillation in the air around the latent fiber strands is believed to be responsible for their unique geometry when made by the melt blowing process.
A great number of variables can contribute to fiber morphology. These may be loosely grouped as dope variables and spinning variables. The dope variables may affect the dope viscosity and may heavily influenced by cellulose degree of polymerization (D.P.). This, in turn, may affect allowable cellulose concentration and ultimate throughput rate. The characteristics of the cellulose itself are important; e.g., the type of pulping process and the subsequent bleaching sequence. These affect not only D.P. but such properties as xcex1-cellulose and hemicellulose as well as ease or difficulty of dissolving the cellulose in the spinning solvent. Solvent composition is also an important factor; e.g., the solvent mixture described in U.S. Pat. No. 5,362,867 will give a lower viscosity dope at a given cellulose concentration than will the NMMO/water mixture. Spinning variables include but are not limited to extrusion head temperature, air temperature, air velocity, the mass ratio of air to dope, dope throughput rate, orifice configuration and the temperature profile along the orifice, and regeneration procedure. Other important variables relate to width of the extrusion head nosepiece; i.e., the distance from nozzle centers to the air exit ports, width and configuration of the air exit ports and angle of the air stream relative to the centerlines of the nozzles. The term xe2x80x9corifice configurationxe2x80x9d refers not only to the orifice itself but includes any lead in capillary section. Orifice diameter and the length/diameter ratio and the presence or absence of a capillary preceding the orifice have been found to be quite important for production of continuous fibers with minimum die swell at the orifice exit.
The present method is capable of production rates of at least 1 g/min of dope per spinning orifice. This is considerably greater than the throughput rate of present commercial processes. Further, the fibers have a tensile strength averaging at least 2 g/denier and can readily be produced within the range of 4-100 xcexcm in diameter, preferably about 5-30 xcexcm. A most preferred fiber diameter is about 9-20 xcexcm, approximately the range of natural cotton fibers. These fibers are especially well suited as textile fibers but could also find applications in filtration media, absorbent products, and nonwoven fabrics as examples.
In the case of the present invention, the pulp may be a high xcex1-cellulose type, generally known as a chemical pulp, or it may be a lower grade pulp. Kraft process pulps have been found satisfactory. The xcex1 value of a pulp is a measure of the amount of xcex1-cellulose present in the pulp, i.e., cellulose composed of glucose monomers. The higher the xcex1 value of a pulp, the higher is the amount of xcex1 cellulose. The xcex1 value of a pulp can be determined by TAPPI test T203OM-88 which is well known to one of ordinary skill in the pulping art. In addition to xcex1-cellulose, pulp also contains hemicelluloses which are branched, low molecular weight polysaccharides associated in the plant cell wall with xcex1-cellulose and lignin. Hemicelluloses are formed from several different monosaccharides, such as mannose, galactose and arabinose. Thus, pulps having a low xcex1 value contain a larger proportion of hemicelluloses compared to pulps having a high xcex1 value.
High xcex1-pulps typically have an xcex1-value of greater than about to 90%, more typically greater than about 94%. Lower grade pulps (low xcex1 pulps) typically have an xcex1-value of less than 90%, usually in the range of from about 83% to about 89%. The ability to use lower xcex1 pulps is a major advantage of the present process since they generally require less expensive processing.
With respect to the degree of polymerization (D.P.) of pulps that are useful in the practice of the present invention, the process of the present invention can utilize a pulp having a D.P. of from about 150 to about 3000; preferably from about 300 to about 1000; most preferably about 600. Fibers formed from pulp having a D.P. at or near the lower end of the foregoing D.P. range will typically have a reduced fiber strength relative to fibers formed from pulp having a higher D.P. Thus, for example, fibers formed from pulp having a D.P. of from about 150 to about 200 will primarily be useful in the manufacture of non-woven materials in which individual fiber strength is not a significant concern.
A preferred pulp useful in the practice of the present invention will be in roll form and will have a low xcex1 value, preferably less than about 90%, and a low D.P., preferably from about 300 to about 1000; most preferably about 600.
The hemicellulose content of the lyocell fibers produced in accordance with the process of the present invention is somewhat less than the hemicellulose content of the cellulosic starting material. Using the preferred pulp of the present invention as a starting material, the resulting lyocell fibers have been observed to have a hemicellulose content of from about 13% to about 15%.
With respect to the concentration of dissolved cellulose utilized in the process of the present invention, in general it is desirable to use a higher concentration of cellulose since a higher concentration of cellulose enables higher cellulose throughput per orifice for a unit of time. On the other hand, it will be understood that the viscosity of a cellulose solution varies directly with the average D.P. of the cellulose, i.e., the higher the D.P., the greater will be the viscosity of the cellulose in solution. Consequently, the useful concentration of a high D.P. pulp will typically be lower than the useful concentration of a low D.P. pulp. Thus, for example, in the practice of the present invention the concentration of cellulose having a D.P. of 3000 will typically be about 1% while the concentration of cellulose having a D.P. of about 150 will typically be from about 25% to about 30%. Again, by way of non-limiting example, in the practice of the present invention the concentration of cellulose having a D.P. of from about 800 to about 1000 will typically be from about 18% to about 20% while the concentration of cellulose having a D.P. of about 600 will typically be from about 8% to about 9%. One of ordinary skill in the pulping art will understand, however, that factors such as the temperature of the dissolved cellulose and the chemical properties of the solvent will also affect the useful concentration of dissolved cellulose.
A preferred starting cellulose material is a bleached kraft market pulp modified to a D.P. range of about 300-1000, most preferably about 600. This permits cellulose concentrations in the dope to range between about 8-18%. Typical kraft market pulps of this type have a D.P. of about 1200-1500. One way the D.P. may be reduced is by acid hydrolysis at any point before, after, or during the bleaching process. Any acid may be utilized, such as hydrochloric acid or sulphuric acid. The acid may be utilized in the form of a liquid, or may be formed from a gas, such as by dissolving hydrogen chloride gas in an aqueous medium. Other known methods of D.P. control are equally suitable. For example, another method is by swelling the cellulose in an alkaline solution followed by alkali removal and treatment with a cellulolytic enzyme, preferably one of the endogluconase types (hereinafter referred to as alkaline enzymatic degradation). Steam explosion may also be utilized Further, a combination of methods of D.P. reduction can be utilized, such as steam explosion combined with acid hydrolysis. An advantage of utilizing acid hydrolysis to reduce D.P. is that transition metal contaminants in the pulp are removed by the acid treatment. If an acid treatment step is not utilized, then an alternative method of removing transition metals from the pulp can be utilized, such as treatment of the pulp with a chelating agent. Although, a preferred starting cellulose material is a bleached kraft market pulp, reduction of D.P. can be effected before, during or after bleaching of the pulp. Preferably, the reduction of degree of polymerization is made such that sufficient fiber is maintained so that the treated pulp can be processed into roll form. However, it is contemplated that treated pulp can be processed into bale form for shipping. Pulps that have been treated to reduce their D.P. in accordance with any of the foregoing methods will typically dissolve faster in amine oxide solvents, such as NMMO with less undesirable gelation.
Spinning orifice diameter may be in the 300-600 xcexcm range, preferably about 400-500 xcexcm. with a L/D ratio in the range of about 2.5-10. Most desirably a lead in capillary of greater diameter than the orifice is used. The capillary will normally be about 1.2-2.5 times the diameter of the orifice and will have a L/D ratio of about 10-250. Commercial lyocell fibers are spun with very small orifices in the range of 60-80 xcexcm. The larger orifice diameters of the present invention are advantageous in that they are one factor allowing much greater throughput per unit of time, throughputs that equal or exceed 1 g/min/orifice. Further, they are not nearly as susceptible to plugging from small bits of foreign matter or undissolved fibers in the dope as are the smaller nozzles. The larger nozzles are much more easily cleaned if plugging should occur and construction of the extrusion heads is considerably simplified. Operating temperature and temperature profile along the orifice and capillary should fall within the range of about 70xc2x0 C. to 140xc2x0 C. It seems beneficial to have a rising temperature near the exit of the spinning orifices. There are many advantages to operation at as high a temperature as possible, up to about 140xc2x0 C. where NMMO begins to decompose. Among these advantages, throughput rate may generally be increased at higher dope temperatures. By profiling orifice temperature, the decomposition temperature may be safely approached at the exit point since the time the dope is held at or near this temperature is very minimal. Air temperature as it exits the melt blowing head is broadly critical and should be in the 40xc2x0-100xc2x0 C. range, preferably about 60xc2x0 C.
Certain defects are known to be associated with melt blowing. xe2x80x9cShotxe2x80x9d is a glob of polymer of significantly larger diameter than the fibers. It principally occurs when a fiber is broken and the end snaps back. Shot is often formed when process rates are high and melt and air temperatures and airflow rates are low. xe2x80x9cFlyxe2x80x9d is a term used to describe short fibers formed on breakage from the polymer stream. xe2x80x9cRopexe2x80x9d is used to describe multiple fibers twisted and usually bonded together. Fly and rope occur at high airflow rates and high die and air temperatures. xe2x80x9cDie swellxe2x80x9d occurs at the exit of the spinning orifices when the emerging polymer stream enlarges to significantly greater diameter than the orifice diameter. This occurs because polymers, particularly molecularly oriented polymers, do not always act as true liquids. When molten polymer streams are held under pressure, expansion occurs upon release of the pressure. Orifice design is critical for controlling die swell.
Melt blowing of thermoplastics has been described by R. L. Shambaugh, Industrial and Engineering Chemistry Research 27:2363-2372 (1988) as operating in three regions. Region I has relatively low gas velocity similar to commercial xe2x80x9cmelt spinningxe2x80x9d operations where fibers are continuous. Region II is an unstable region which occurs as gas velocity is increased. The filaments break up into fiber segments. Region III occurs at very high air velocities with excessive fiber breakage. In the present process air velocity, air mass flow and temperature, and dope mass flow and temperature are chosen to give operation in Region I as above described where a shot free product of individual continuous fibers in a wide range of deniers can be formed. The operating conditions in French Patent application 2,735,794, noted earlier, appear to be high in Region II or possibly into Region III.
The extruded latent fiber filaments carried by the gas stream are preferably regenerated by a fine water spray during the later part of their trajectory. They are received on a take-up roll or moving foraminous belt where they may be transported for further processing. The take-up roll or belt will normally be operated at a speed somewhat lower than that of the arriving fibers so that there is no or only minimal tension placed on the arriving fibers.
Filaments having an average size as low as 0.1 denier or even less can be readily formed. Denier can be controlled by a number of factors including but not limited to orifice diameter, gas stream speed, dope viscosity and throughput rate. Dope viscosity is, in turn, largely a factor of cellulose D.P. and concentration. Gloss or luster of the fibers is considerably lower than continuously drawn lyocell fiber lacking a delusterant so they do not have a xe2x80x9cplasticxe2x80x9d appearance. This is believed to be due to their unique xe2x80x9cpebbledxe2x80x9d surface apparent in high magnification scanning electron micrographs.
By properly controlling spinning conditions the fibers can be formed with variable cross sectional shape and a relatively narrow distribution of fiber diameters. Some variation in diameter and cross sectional configuration will typically occur along the length of individual fibers and between fibers. The fibers are unique for regenerated cellulose and similar in morphology to many natural fibers.
Fibers produced by the melt blowing process possess a natural crimp quite unlike that imparted by a stuffer box. Crimp imparted by a stuffer box is relatively regular, has a relatively low amplitude, usually less than one fiber diameter, and short peak-to-peak period normally not more than two or three fiber diameters. That of the present fibers has an irregular amplitude usually greater than one fiber diameter and an irregular period usually exceeding about five fiber diameters, a characteristic of fibers having a curly or wavy appearance.
Quite unexpectedly, the fibers of the present invention appear to be highly resistant to fibrillation under conditions of wet abrasion. This is a major advantage in that no post-spinning processing is required, such as crosslinking or enzymatic treatment.
Properties of the fibers of the present invention are well matched for carding and spinning or knitting in conventional textile manufacturing processes. The fibers have many of the attributes of natural fibers. They have been found to accept dyes exceptionally well.
The process is particularly well suited for making lyocell fiber in the 5-30 xcexcm diameter range at throughputs that equal or exceed at least 1 g of dope per minute per spinning orifice. It is particularly well suited for making fiber in the 10-20 xcexcm cotton denier range. Fiber average strength has been found to equal or exceed about 2 g/denier.
A particular advantage of the present invention is the ability to form blends of cellulose with what might otherwise be considered as incompatible polymeric materials. The amine oxides are extremely powerful solvents and can dissolve many other polymers beside cellulose. It is thus possible to form blends of cellulose with materials such as lignin, nylons, polyethylene oxides, polypropylene oxides, poly(acrylonitrile), poly(vinylpyrrolidone), poly(acrylic acid), starches, poly(vinyl alcohol), polyesters, polyketones, casein, cellulose acetate, amylose, amylopectins, cationic starches, and many others. Each of these materials in homogeneous blends with cellulose can produce fibers having new and unique properties.
It is an object of the present invention to provide a method of forming regenerated cellulose fibers or cellulose blend fibers from solution in an amine oxide-water or other solvent by a process analogous to melt blowing.
It is a further object to provide a method for making lyocell fibers having advantageous geometry and surface characteristics for forming into yarns.
It is still an object to provide a method for making lyocell fibers having natural crimp and low luster.
It is an additional object to provide a method for forming a lyocell fiber resistant to fibrillation under conditions of wet abrasion.
It is yet an object to provide a method of forming fibers of the above types by a process in which all production chemicals can be readily recovered and reused.
It is an important object to provide lyocell fibers having superior dyeing characteristics.
It is also an object to provide regenerated cellulose fibers having many properties similar or superior to natural fibers.
A farther object is to provide a method of lyocell fiber production at a high rate of throughput per spinning orifice.
Yet another object is to provide a method of production of lyocell fibers in which fiber production is not normally interrupted by small air bubbles or foreign matter which might cause fiber breaks.
Another object of the present invention is to make lyocell fibers having a hemicellulose contents of from about 13% to about 15%.
These and many other objects will become readily apparent to those skilled in the art upon reading the following detailed description in conjunction with referral to the drawings.